Some biological molecules are sufficiently stable that they can be isolated, purified and then stored in solution at room temperature. However, this is not possible for many materials and techniques involving storage at low temperature, addition of stabilizers or cryoprotectants, freeze-drying, vacuum-drying and air-drying have been tried to ensure shelf preservation.
Despite the availability of these techniques, some biological materials still show unsatisfactory levels of stability during storage and some techniques lead to added cost and inconvenience. For example, refrigerated transportation and storage is expensive, and any breaks in temperature control can result in reduced efficacy of the biological molecule. Further, refrigerated transport is often not available for the transport of medicines in countries in the developing world.
Also, the stresses of freeze-drying or lyophilisation can be very damaging to some biological materials. Freeze drying of biopharmaceuticals involves freezing solutions or suspensions of thermosensitive biomaterials, followed by primary and secondary drying. The technique is based on sublimation of water at subzero temperature under vacuum without the solution melting. Freeze-drying represents a key step for manufacturing solid protein and vaccine pharmaceuticals. The rate of water vapour diffusion from the frozen biomaterial is very low and therefore the process is time-consuming. Additionally, both the freezing and drying stages introduce stresses that are capable of unfolding or denaturing proteins.
WO 90/05182 describes a method of protecting proteins against denaturation on drying. The method comprises the steps of mixing an aqueous solution of the protein with a soluble cationic polyelectrolyte and a cyclic polyol and removing water from the solution. Diethylaminoethyldextran (DEAE-dextran) and chitosan are the preferred cationic polyelectrolytes, although polyethyleneimine is also mentioned as suitable.
WO-A-2006/0850082 reports a desiccated or preserved product comprising a sugar, a charged material such as a histone protein and a desiccation- or thermosensitive biological component. The sugar forms an amorphous solid matrix. However, the histone may have immunological consequences if the preserved biological component is administered to a human or animal.
WO 2008/114021 describes a method for preserving viral particles. The method comprises drying an aqueous solution of one or more sugars, a polyethyleneimine and the viral particles to form an amorphous solid matrix comprising the viral particles. The aqueous solution contains the polyethyleneimine at a concentration of 15 μM or less based on the number-average molar mass (Mn) of the polyethyleneimine and the sugar concentration or, if more than one sugar is present, total sugar concentration is greater than 0.1M.